How to use
- Pick a version. Use v4 unless you need IDs that sort by creation time (database primary keys, for example), in which case use v7.
- Enter how many you need (1 to 1,000) and they’re generated right away. Generate new gives you a fresh batch.
- Choose uppercase, no hyphens or braces
{ }, then Copy or download a.txtfile with one UUID per line. - Paste any UUID into Inspect a UUID to see its version and variant, and for v1, v6 and v7, the timestamp embedded in it.
UUID layout and versions
A UUID (RFC 9562, formerly RFC 4122) is a 128-bit value written as 36 hex characters in 8-4-4-4-12 groups. The first character of the third group is the version; the first character of the fourth group (8, 9, a or b) marks the standard variant.
| Version | How it’s built | Notes |
|---|---|---|
| v1 | Timestamp (100 ns ticks) + node (MAC address) | Reveals machine and time |
| v4 | 122 random bits | Most common, no ordering |
| v6 | v1 with the time fields reordered for sorting | When you need v1 compatibility |
| v7 | 48-bit Unix time in ms + 74 random bits | Sorts in creation order |
In the v7 example 017f22e2-79b0-7cc3-98c4-dc0c0c07398f, the first 12 hex digits 017f22e279b0 equal 1,645,557,742,000 ms — 2022-02-22 19:22:22 UTC (the example from RFC 9562’s appendix).
v4 or v7?
- v4 when the ID must reveal nothing, such as IDs in public URLs. With 122 random bits, the chance of any collision among a billion IDs is around 10⁻¹⁹.
- v7 for primary keys and log IDs where order matters. New values land at the end of the index, which reduces B-tree fragmentation. The creation time (to the millisecond) is visible, though, so don’t use it where that would leak information.
- This tool’s v7 uses the counter method from RFC 9562 §6.2, so IDs created within the same millisecond still sort in order.
FAQ
Is a GUID different from a UUID?
They’re the same thing. GUID is Microsoft’s name for it, and Windows and .NET often show it in uppercase with braces ({...}), which you can produce with the options above.
Are generated UUIDs stored anywhere?
No. They’re created on your device with the browser’s cryptographic random number generator (crypto.getRandomValues, or crypto.randomUUID where available) and never sent or logged. For a secret a human has to type, the Password Generator is a better fit. To check a v7 timestamp on its own, paste the millisecond value into the Unix Timestamp Converter.